In mobile communications, a spread spectrum communication with high frequency utilization efficiency capable of high-speed and high quality data communication, a CDMA (Code Division Multiple Access) system in particular, is becoming mainstream in recent years.
An area covered by one base station is called a “cell”. If it is possible to increase the radius of a cell, the number of base stations can be reduced. Thus, the radius of a cell is an important factor in a mobile communication system and the radius of a cell may actually extend a few tens of km.
In the case where the radius of a cell reaches a few tens of kin, the distance from a mobile unit to a base station varies a great deal when the mobile unit is close to the base station and when the mobile unit is located. near the cell boundary. Therefore, the amount of delay of a signal received by the base station varies a great deal.
When a CDMA-based mobile communication between a mobile terminal apparatus and a base station starts, the base station needs to carry out high-speed initial synchronization processing taking into account a sufficiently large radius of a cell first.
For example, when the mobile terminal apparatus requests the base station, which is the communication target, for a communication permission, the base station learns how far the mobile terminal apparatus is located by measuring a propagation delay time relative to a reference signal.
That is, it is possible to know a rough distance to the mobile station by the base station sending a reference signal to the mobile station at a predetermined timing (reference timing) and measuring a time (this corresponding to a propagation delay time) required for an ACK (acknowledge signal) to be sent from the mobile station in response thereto. As a result, the base station can narrow the search range of correlation detection to a certain degree when detecting an acknowledge signal from the mobile station in response to the signal sent from the base station.
The propagation delay time is calculated with reference to delay profile information obtained by a matched filter circuit.
When creating a delay profile, the matched filter carries out a so-called data scan/code fixed despreading calculation. That is, a spreading code necessary for a despreading calculation of a target symbol is set (code-fixed) in the matched filter and a correlation value is calculated by inputting reception data continuously over a search segment which is determined with a propagation delay time taken into account.
FIG. 21 shows a configuration of a conventional matched filter.
Spreading codes generated by code generator 106 are stored in code register 107. Code register 107 consists of 256 shift registers 104b. 
Then, reception data is input serially to shift register 105. Every time 1-chip reception data is input, despreading calculation section 109 multiplies the parallel outputs of shift register 105 by the outputs of code register 107. Despreading calculation section 109 consists of 256 multiplication circuits 108.
Then, integrating calculation segment 103 (provided with integration circuit 110) integrates the parallel outputs of despreading calculation section 109 and calculates a correlation value corresponding to 1-symbol data.
Suppose the search range (width of delay time) is 0 to 255 chips (equivalent to 1 symbol). Since the above calculation is carried out every time data is shifted by one chip, 256 calculations in total are required.
Since the matched filter detects a correlation on a symbol-by-symbol basis, one matched filter can process only a reception signal with a 1-symbol propagation delay.
Here, because of a large radius of a cell, if the search range (width of delay time) extends from 0 to 511 chips (equivalent to 2 symbols), one matched filter is not enough, and therefore two matched filters 9004 and 906 are used as shown in FIG. 22A.
The two matched filters 904 and 906 in FIG. 22A operate at reference timings which are different from each other and both matched filters output a delay profile equivalent to one symbol.
FIG. 22B is a timing chart to illustrate operations of the two matched filters.
As shown in the figure, matched filter 904 operates at a first reference timing and matched filter 906 operates at a second reference timing with a delay time equivalent to one symbol.
An operation of each matched filter will be explained taking processing of the first symbol as an example.
At time T1, a first symbol spreading code is set in matched filter 904 and a correlation calculation on the first symbol is performed while shifting the input data one chip at a time. A search from chip 0 to chip 255 (first-half search) finishes at time T2.
Then, at time T2 (second reference timing), a first symbol spreading code is set in matched filter 906 and a correlation calculation on the first symbol is performed while shifting the input data one chip at a time until time T3. A search from chip 256 to chip 511 (last-half search) finishes at time T3.
At time T2, a second symbol detection code is set in matched filter 904 and a search on the second symbol starts.
By combining the search results from chip 0 to chip 255 and the search results from chip 256 to chip 511 on the first symbol calculated in this way together, it is possible to obtain a delay profile with a time equivalent to two symbols with respect to the first symbol.
However, the use of a plurality of matched filters will increase the scale of the circuit and extremely increase power consumption as well. That is, as the area occupied by the LSI chip increases, both costs and current consumption increase accordingly.
In reality, however, the radius of a cell (coverage) tends to necessarily be increased, which also causes propagation delays to increase, and covering those propagation delays needs to further increase the number of matched filters.
Moreover, mobile terminal apparatuses and base stations actually use a plurality of matched filters to generate and calculate delay profiles under various conditions. In this case, an increase of the scale of the circuit and increase of cost and power consumption constitute problems, too.
As shown above, since conventional matched filters have low processing performance, it is difficult to meet current demands by correlation detection using those matched filters.
It is an object of the present invention to improve by far the efficiency (processing speed) of correlation detection processing using matched filters and thereby suppress increases of the scale of the circuit and solve the problems of power consumption.
That is, use of the present invention basically allows a single matched filter to even handle cases where a base station has a large radius of a cell or where mobile stations calculate delay profiles under multiple conditions.